+1 To all the wonderful advice given o:
To add a little more about the heater.....I use them for my 2-ish gallons; I wouldn't recommend them for anything bigger, and only in the smaller tank if the room they are kept in has a fairly warm/stable temperature as they are not adjustable/can't be turned off/and only heat a few degrees above room temp.
I attempted one in a 5 gallon a couple of years back; it hardly raised the temp two degrees and my room was fairly warm and stable.
I highly recommend a 25-50 watt adjustable, submersible heater. In my five gallon I currently have this
, and when I had my larger tanks set up I used the same brand. They may be a little more on the pricey side, but they're good quality and I'm very happy with mine.
As for the cycling....no, you don't have to cycle before getting your fish, as stated previously, but regardless, so long as you have a filter running, your tank will
go through a cycle(you can very easily just turn the filter off/remove it if you'd rather just do the slightly more frequent weekly changes and not bother cycling though).
^ A neat little page that explains the cycling process. Take a look and you can decide if you'd like to mess with it or not. ;)
I wish you the best of luck with your future new fishy friend, and cookies to you for doing your research and getting a properly-sized heated tank! :) And, as always, feel free to ask if you have any further questions of concerns.